Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

D366 ammonium measurements from CTD rosette bottle samples

Originator's Protocol for Data Acquisition and Analysis

Samples for water column measurements of ammonium were taken from the 20 L Niskin bottles deployed on the stainless steel CTD rosette frame. Samples were taken on a daily basis, and all CTD stations were covered. Samples for ammonium were collected in polypropylene vials and reagent added, with subsequent fluorimetric analysis 24 h later. The method by Kerouel and Aminot (1997) was followed, allowing nanomolar ammonium concentrations to be determined. Typically 6-12 depths were covered for a CTD cast.

References Cited

BODC Data Processing Procedures

Data were submitted after the cruise and archived under BODC's accession number USO130151. The ammonium data were provided in a file with sample metadata (station, cast number, date and depth). The data were matched to the metadata in the database based on cast/depth combinations. A number of discrepancies were discovered and queried with the originator. A revised data file was received with these discrepancies resolved. In addition there was a corrected version of data for cast 68.

No unit conversion was necessary as the data were provided in equivalent units to the assigned BODC parameter code. The data were loaded to the database using established BODC procedures.

Problem Report

The overall aim of this theme is to obtain a quantitative understanding of the impact of ocean acidification (OA) on the surface ocean biology and ecosystem and on the role of the surface ocean within the overall Earth System.

The aims of the theme are:

To ascertain the impact of OA on planktonic organisms (in terms of physiological impacts, morphology, population abundances and community composition).

To quantify the impacts of OA on biogeochemical processes affecting the ocean carbon cycle (both directly and indirectly, such as via availability of bio-limiting nutrients).

To quantify the impacts of OA on the air-sea flux of climate active gases (DMS and N2O in particular).

The main consortium activities will consist of in-situ measurements on three dedicated cruises, as well as on-deck bioassay experiments probing the response of the in-situ community to elevated CO2. Most of the planned work will be carried out on the three cruises to locations with strong gradients in seawater carbon chemistry and pH; the Arctic Ocean, around the British Isles and the Southern Ocean.